Backports for 0.25.3 (#29313)

* Backport PR #27826 for 0.25.3 release

* BUG: Fix groupby quantile segfault

Validate that q is between 0 and 1.

Closes #27470

* prettier

* Backport PR #29173 for 0.25.3 release

* Backport PR #29296 for 0.25.3 release

* Backport PR #29294 for 0.25.3 whatsnew

Author: WillAyd

Diff for: doc/source/whatsnew/index.rst

@@ -16,6 +16,7 @@ Version 0.25
 .. toctree::
    :maxdepth: 2
 
+   v0.25.3
    v0.25.2
    v0.25.1
    v0.25.0

Diff for: doc/source/whatsnew/v0.25.3.rst

@@ -0,0 +1,22 @@
+.. _whatsnew_0253:
+
+What's new in 0.25.3 (October 31, 2019)
+---------------------------------------
+
+These are the changes in pandas 0.25.3. See :ref:`release` for a full changelog
+including other versions of pandas.
+
+.. _whatsnew_0253.bug_fixes:
+
+Bug fixes
+~~~~~~~~~
+
+Groupby/resample/rolling
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+- Bug in :meth:`DataFrameGroupBy.quantile` where NA values in the grouping could cause segfaults or incorrect results (:issue:`28882`)
+
+Contributors
+~~~~~~~~~~~~
+
+.. contributors:: v0.25.2..HEAD

Diff for: pandas/_libs/groupby.pyx

@@ -719,6 +719,11 @@ def group_quantile(ndarray[float64_t] out,
         ndarray[int64_t] counts, non_na_counts, sort_arr
 
     assert values.shape[0] == N
+
+    if not (0 <= q <= 1):
+        raise ValueError("'q' must be between 0 and 1. Got"
+                         " '{}' instead".format(q))
+
     inter_methods = {
         'linear': INTERPOLATION_LINEAR,
         'lower': INTERPOLATION_LOWER,
@@ -736,6 +741,9 @@ def group_quantile(ndarray[float64_t] out,
     with nogil:
         for i in range(N):
             lab = labels[i]
+            if lab == -1:  # NA group label
+                continue
+
             counts[lab] += 1
             if not mask[i]:
                 non_na_counts[lab] += 1

Diff for: pandas/io/parsers.py

@@ -2935,7 +2935,7 @@ def _next_iter_line(self, row_num):
             if self.warn_bad_lines or self.error_bad_lines:
                 msg = str(e)
 
-                if "NULL byte" in msg:
+                if "NULL byte" in msg or "line contains NUL" in msg:
                     msg = (
                         "NULL byte detected. This byte "
                         "cannot be processed in Python's "

Diff for: pandas/tests/groupby/test_function.py

@@ -1316,6 +1316,40 @@ def test_quantile_raises():
         df.groupby("key").quantile()
 
 
+def test_quantile_out_of_bounds_q_raises():
+    # https://github.com/pandas-dev/pandas/issues/27470
+    df = pd.DataFrame(dict(a=[0, 0, 0, 1, 1, 1], b=range(6)))
+    g = df.groupby([0, 0, 0, 1, 1, 1])
+    with pytest.raises(ValueError, match="Got '50.0' instead"):
+        g.quantile(50)
+
+    with pytest.raises(ValueError, match="Got '-1.0' instead"):
+        g.quantile(-1)
+
+
+def test_quantile_missing_group_values_no_segfaults():
+    # GH 28662
+    data = np.array([1.0, np.nan, 1.0])
+    df = pd.DataFrame(dict(key=data, val=range(3)))
+
+    # Random segfaults; would have been guaranteed in loop
+    grp = df.groupby("key")
+    for _ in range(100):
+        grp.quantile()
+
+
+def test_quantile_missing_group_values_correct_results():
+    # GH 28662
+    data = np.array([1.0, np.nan, 3.0, np.nan])
+    df = pd.DataFrame(dict(key=data, val=range(4)))
+
+    result = df.groupby("key").quantile()
+    expected = pd.DataFrame(
+        [1.0, 3.0], index=pd.Index([1.0, 3.0], name="key"), columns=["val"]
+    )
+    tm.assert_frame_equal(result, expected)
+
+
 # pipe
 # --------------------------------
 

Diff for: pandas/tests/io/parser/test_common.py

@@ -1898,10 +1898,7 @@ def test_null_byte_char(all_parsers):
         out = parser.read_csv(StringIO(data), names=names)
         tm.assert_frame_equal(out, expected)
     else:
-        if compat.PY38:
-            msg = "line contains NUL"
-        else:
-            msg = "NULL byte detected"
+        msg = "NULL byte detected"
         with pytest.raises(ParserError, match=msg):
             parser.read_csv(StringIO(data), names=names)